If you want a subset of your users to have access to your vsftpd FTP server, edit /etc/vsftpd.conf adding the following:

# Activate only users in /etc/vsftpd.enabledusers
userlist_deny=NO
userlist_enable=YES
userlist_file=/etc/vsftpd.enabledusers

The file /etc/vsftpd.enabledusers must contain the list of users enabled to access the FTP service, one per line. Be sure to also add the support for local users:

local_enable=YES

You may also want to fix the home directory, for example to /var/www/:

local_root=/var/www